This invention relates to die attach adhesives with improved adhesion due to the presence of epoxy compound or resin with allyl or vinyl unsaturation.
Adhesive compositions are used for a variety of purposes in the fabrication and assembly of semiconductor packages, such as, the bonding of integrated circuit chips to leadframes or other substrates, and the bonding of circuit packages or assemblies to printed wire boards. Major requirements for these uses are fast cure and high adhesive strength, traditionally achieved with epoxy resins. Epoxy resins, however, can be brittle, and other resins have been evaluated and employed to bring flexibility, hydrophobicity, and other properties to die attach adhesives. The alternate resins, in turn, do not always display the strong adhesion provided by the epoxy resins. Therefore, there is a need for die attach adhesives that incorporate a balance of properties to meet all the requirements for an adhesive used in the manufacture of a semiconductor package.
This invention is an adhesive composition comprising (a) a compound or resin that will cure by free-radical polymerization, that is, one having carbon to carbon unsaturation, or that will cure by hydrosilation, that is, one having silicon-hydride groups, (b) an epoxy compound that contains allyl or vinyl unsaturation, (c) a curing agent for the compound or resin (a) and a curing agent for the epoxy compound or resin (b), and (d) optionally, one or more fillers. The composition may also contain adhesion promoters or coupling agents. The inventors discovered that the addition of the epoxy compound containing allyl or vinyl unsaturation gave an unexpected increase in adhesion performance to the base compound or resin containing the carbon to carbon unsaturation. In another embodiment, this invention is a semiconductor package having a semiconductor die adhered to a substrate with the inventive adhesive.
Free-radical curable compounds or resins, which can be used as adhesives in microelectronic applications, include, for example, maleimides, such as those available from Ciba Specialty Chemicals; siloxanes and polysiloxanes, such as those available from from Gelest; polyethers, such as those available from from BASF; polyesters, such as those available from from Uniqema or Bayer; poly(butadiene)s, such as those available from from Elf-Atochem; polyurethanes, such as those available from from Bayer or BASF; and acrylate resins, such as those available from from Sartomer or UCB Radcure. Siloxanes and polysiloxanes, which cure by hydrosilation, may be linear or cylic polymers, and will have at least 2 silicone-hydride functionalities per molecule. The polyethers, polyesters, and polyurethanes preferably will contain terminal unsaturation, but may also contain unsaturation within the polymer chain. The particular compound or resin will be chosen by the practitioner to give specific material properties in a final formulation, such as, rheological properties, hydrophilic or hydrophobic properties, toughness, strength, or flexibility. The compound or resin will be present in the adhesive composition in a range of 10-80% by weight.
The epoxy compounds or resins may be any with allyl or vinyl functionality. Examples include 2,6-digylcidylphenyl allyl ether, glycidyl vinyl benzyl ether or glycidyl vinyl ether. The epoxy will be present in the adhesive composition in a range of 0.1-30% by weight.
Exemplary curing agents for the base compounds or resins are free-radical initiators, which can be thermal- or photo-Initiators. The initiators will be present in the adhesive composition in an amount of 0.1% to 10%, preferably 0.1% to 3.0%, by weight. Preferred thermal initiators Include peroxides, such as butyl peroctoates and dicumyl peroxide, and azo compounds, such as 2,2xe2x80x2-azobis(2-methyl-propanenitrile) and 2,2xe2x80x2-azobis(2-methyl-butanenitrile). A preferred series of photoinitiator is one sold under the trademark Irgacure by Ciba Specialty Chemicals. In some formulations, both photocure and thermal cure may be desirable, for example, the curing process can be started by irradiation, and in a later processing step curing can be completed by the application of heat.
Exemplary curing agents for the epoxy functionality on the epoxy compound or resin are Lewis bases, for example, amines, such as Ancamine 2337xs, and 4,4xe2x80x2-bis(para amino cyclohexyl)methane, both commercially available from Air Products; imidazoles, such as Curezol 2E4MZ-CN, a product of Shikoku Chemicals; amides, such as, Dicyanamide, a product of Air Products; polyamides, such as Versamide 140, a product of Henkel; tertiary amines, such as Amicure DBU, a product of Air Products. Alternatively, Lewis acids, such as Rhodorasll 2074[(tolylcumyl)iodonium tetrakis(pentafluorophenyl)borate], a product of Rhodia, or GE UV9380C, a product of General Electric, can be used to initiate a cationic cure. The curing agent for the epoxy functionality will be present in the composition in a range of 0.1 to 3% by weight of the total formulation,
In general, these compositions will cure within a temperature range of 70xc2x0 C. to 250xc2x0 C., and curing will be effected within a range of ten seconds to three hours. The time and temperature curing profile of each formulation will vary with the components of the formulation, but the parameters of a curing profile can be adjusted by a practitioner skilled in the art without undue experimentation.
In some compositions it may be desirable to add organic or inorganic fillers. Suitable conductive fillers are carbon black, graphite, gold, silver, copper, platinum, palladium, nickel, aluminum, silicon carbide, boron nitride, diamond, and alumina. Suitable nonconductive fillers are particles of vermiculite, mica, wollastonite, calcium carbonate, titania, sand, glass, fused silica, fumed silica, barium sulfate, and halogenated ethylene polymers, such as tetrafluoroethylene, trifluoroethylene, vinylidene fluoride, vinyl fluoride, vinylidene chloride, and vinyl chloride. Although optional, when present, fillers will be in amounts of 20% to 90% by weight of the composition.
Suitable adhesion promoters or coupling agents are silanes, silicate esters, metal acrylates or methacrylates, titanates, and compounds containing a chelating ligand, such as phosphine, mercaptan, and acetoacetate. When present, coupling agents will be in amounts up to 10% by weight, and preferably in amounts of 0.1% to 3.0% percent by weight.
The invention is further illustrated by the following examples, which are not intended as a limitation on the invention.